The present invention relates to a printer for forming images on a web transported at high speed; and, more particularly, the invention relates to a printer capable of stably transporting a web at high speed, even if a web having no feeding perforations is used.
In a printer capable of forming images on a web, in general, the web is transported by engaging pin members of a tractor mechanism mounted on the printer with feeding perforations disposed along the margins of the web. The tractor mechanism is then driven, and, at the same time, images are formed on the web at an image forming portion of the printer. However, in the case of printing on a web with feeding perforations, work for cutting off the perforated portions (usually, both marginal edge portions in the width direction of the web) from the web is necessary after the printing, and, accordingly, it takes an additional time to obtain the final printed matter. Further, the printer inevitably must be equipped with a tractor mechanism, which makes the structure of the printer complex. The cutting-off work described above can be eliminated by employing a web without feeding perforations and by changing the web transporting unit in the printer from that of a tractor mechanism to that of a transporting roller mechanism.
In a printer which forms images on a web that does not have feeding perforations, such as by transporting the web using a transporting roller mechanism, if the printer is a printer operating in a middle speed range up to a speed equivalent to the transporting speed of 50 pages/minute of A4-size paper in landscape configuration, significant slipping does not occur between the web and the transporting roller, and printing with little misalignment of position can be performed.
However, in a printer operating in a high speed range having a printing speed above 100 pages/minute, or in a printer operating in an ultra-high speed range having a printing speed above 200 pages/minute, using the conventional structure, it is difficult to correctly transport the web to the printing portion. Therefore, it is necessary to highly accurately control the tension and the traveling position of the web during transporting of the web.
An object of the present invention is to provide a printer which is capable of stably transporting a web at high speed and with high accuracy.
The above object can be attained by a printer for forming an image on a transported web, which comprises a printing unit for forming the image on the web; a yet-to-be-printed web control means for controlling the traveling position and the tension of the web at a position upstream in a web transporting direction of the printing unit; and an after-printed web control means for controlling the traveling position and the tension of the web at a position downstream in the web transporting direction of the printing unit.